The PCMCIA card has found its way into virtually every computer related application ranging from flash memories to handheld medical equipment. The PCMCIA card may be plugged into a host device, such as a portable computer, with a standard 68-pin connector. In a typical PCMCIA system, the host device contains 3.3, 5, and 12 volt power supplies, a PCMCIA controller, and a PCMCIA power interface device. The PCMCIA controller polls the PCMCIA card via an I/O bus to determine which voltages the card requires at its V.sub.pp and V.sub.cc pins and transmits this information to the power interface device via a control bus. In response thereto, the power interface device provides the requested voltages to the PCMCIA card at the V.sub.pp and V.sub.cc pins. The operating voltages are provided at the V.sub.cc pin while the read, write, and erase voltages are provided at the V.sub.pp pin. In accordance with PCMCIA standards, the power interface device must selectively distribute voltages of 0, 3.3, and 5 volts to the V.sub.cc pins and 0, 3.3, 5.0, and 12 volts to the V.sub.pp pins.
The PCMCIA convention requires that the power interface device utilizes high-side switching, i.e., all loads are hard wired to ground and the on/off state of each load is controlled with a switch connected between the load's supply inputs and an external DC power source. For low current applications, a P-channel device may be used as the switch. Due to the relatively high on-resistance of P-channel devices as compared to that of N-channel devices, however, high current applications require a N-channel switch. An inherently slow charge pump circuit capable of bringing the gate of the N-channel switch approximately 10 volts or more above its source is normally used to turn on the N-channel switches.
Accordingly, PCMCIA power interface devices generally include N-channel power MOSFET switches for managing the distribution of voltages to the V.sub.cc and V.sub.pp pins. These MOSFET switches should be turned on gradually to prevent undesirable current spikes which, if not minimized, may pull down the host device's power supply and cause indeterminate states in the interface device's logic. Nonetheless, unless care is taken, conventional interface devices experience some current spikes during switching-of the V.sub.cc line, e.g., switching the V.sub.cc pin from 5 volts to 3.3 volts.
Furthermore, conventional interface devices suffer from breakdown. Although the gate oxide of power MOSFET switches will typically rupture only at high voltages, these MOSFETs may experience degraded performance if subjected to lower voltages for an extended period of time. This phenomenon, sometimes referred to as time dependent breakdown, may cause long term reliability problems in power interface devices.